Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and Personal Digital Assistants (PDAs), for example, incorporate microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as they become smaller and produce better images with more pixels.
Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other solid-state systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also quickly becoming very popular because they are expected to have low production costs, high yields, and small sizes. CMOS image sensors can provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect delicate components and to provide external electrical contacts.
FIG. 1 is a schematic side cross-sectional view of a conventional microelectronic imaging unit 1 including an imaging die 10, a chip carrier 30 carrying the die 10, and a cover 40 attached to the chip carrier 30 and positioned over the die 10. The imaging die 10 includes an image sensor 12 and a plurality of bond-pads 16 operably coupled to the image sensor 12. The chip carrier 30 has a base 32, sidewalls 34 projecting from the base 32, and a recess defined by the base 32 and sidewalls 34. The die 10 is received within the recess and attached to the base 32. The chip carrier 30 further includes an array of terminals 18 on the base 32, an array of contacts 24 on an external surface 38, and a plurality of traces 22 electrically connecting the terminals 18 to corresponding external contacts 24. The terminals 18 are positioned between the die 10 and the sidewalls 34 so that wire-bonds 20 can electrically couple the terminals 18 to corresponding bond-pads 16 on the die 10.
One problem with the microelectronic imaging unit 1 illustrated in FIG. 1 is that the die 10 must fit within the recess of the chip carrier 30. Dies having different shapes and/or sizes accordingly require chip carriers configured to house those specific types of dies. As such, manufacturing imaging units with dies having different sizes requires fabricating various configurations of chip carriers and significantly retooling the manufacturing process.
Another problem with conventional microelectronic imaging units is that they have relatively large footprints. For example, the footprint of the imaging unit 1 in FIG. 1 is the surface area of the base 32 of the chip carrier 30, which is significantly larger than the surface area of the die 10. Accordingly, the footprint of conventional microelectronic imaging units can be a limiting factor in the design and marketability of picture cell phones or PDAs because these devices are continually being made smaller in order to be more portable. Therefore, there is a need to provide microelectronic imaging units with smaller footprints.
The imager 1 shown in FIG. 1 also has an optics unit including a support 50 attached to the chip carrier 30 and a lens system with a plurality of lenses 70 (identified individually by reference numbers 70a-c). Traditional lens systems include a plurality of lenses for focusing the image at the image sensor 12. Traditional lens systems accordingly flatten the field of the image at the image sensor 12 so that the image is focused across the face of the image sensor 12. In the embodiment shown in FIG. 1, for example, the lens 70c may flatten the image “I” across the face of the image sensor 12. In other conventional systems, one or more of the lenses 70a-c can be combined into a single aspherical lens that can focus and flatten an image.
Another problem with conventional microelectronic imaging units that lens systems with multiple lenses or more complex aspherical lenses are relatively tall and complex. Conventional lens systems accordingly have high profiles, can be expensive to manufacture, and may be difficult to assemble. Therefore, it would be desirable to reduce the demands and complexity of lens systems in the manufacturing of microelectronic imagers.